<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let num = +prompt('请输入空瓶的个数')
      let sum = 0
      function getBottom(num) {
        // console.log(Math.floor(num / 3))
        // console.log(num % 3)

        while (true) {
          if (num >= 3) {
            sum += Math.floor(num / 3)
          } else if (num == 2) {
             sum++
             return sum
             break
          } else {
            return sum
            break
          }

          num = Math.floor(num / 3) + (num % 3)
        }
      }
      const res = getBottom(num)
      console.log(res)
    </script>
  </body>
</html>
